OK Dumb Question for someone who has been arround a while :)
GeoffL
the tires did not come with any road hazzard warranty (That was an extra $10
a tire.. How dumb do I feel) So I mounted one of the original 30" GSA's as
the spare.
Now to my question, How bad is it to run 31" tires with a 30" spare??
Assuming that the spare is for "Emergencies" only, is this any worse than
having a small doughnut spare on a car??
I was planning on going wheeling next weekend and I don't know if I will be
able to find a 31" tire for a spare before then. ( Most likly I will need
the spare if I try do the tree run again. Right Mike :)
Thanks to all
GeoffL
98 TJ Sport
P.S. If anyone in the Montreal or Toronto area has 1 31" tire that could be
used as a spare let me know
Mike Romain
As you noted, the difference is minimal compared to the mini spare that
came with our Cherokee.
If you have the limited slip rear, the spare would be best used on the
front, otherwise there shouldn't be any issues.
I do have an extra P235 on a Jeep rim here as a second spare for my
Cherokee, so if you really got stuck...
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:
Easter/02 http://www.imagestation.com/album/?id=4291929351
Jan/02 http://www.imagestation.com/album/?id=4292141347
Aug/01 http://www.imagestation.com/album/?id=4292076845
Day Trip Misc. http://www.imagestation.com/album/?id=4291902217
Zodiac
some sag, then run the 30" spare at regular pressure. The lower pressure in
the other tire should make it close in size to the 30", which should not
throw the diff off.
Donuts on passenger cars are inflated to close to 50 or 60 PSI to get them
close to the size of the regular tires, this is the same principle without
overstressing the 30" spare.
+-=Z=-+
"GeoffL" <lawr...@attcanada.net> wrote in message
news:038N8.3064$H67....@tor-nn1.netcom.ca...
Evan
I have never had same size spair, but never ran the spare for any amount of
time,
01 sahara D44 but outher wise stock (for now)
give it time,
Sorry about the spelling, I'm Dyslexic
Take out the "XXX" to e-mail me
L.W.(Bill) Hughes III
the distance traveled per rotation.
God Bless America, Bill O|||||||O
mailto:LWHug...@aol.com http://www.billhughes.com/
Mike Romain
how hard you pump it up. ;-)
My wife managed to blow a 1 week old AT tire off the rim out at the
place where Geoffl is coming and we had to run that silly tire to get
out and run the 50 miles home after. We now have a full size spare....
Mike
ZJ Driver
minimal, they said I should try not to go to far. Probably not a problem,
but not something you want to do for the long run.
"Mike Romain" <rom...@sympatico.ca> wrote in message
news:3D05139B...@sympatico.ca...
Jerry Bransford
its circumference.
GeoffL, so long as you don't have a Tracloc or other limited slip or
locker, you can run mixed tire sizes without problem while you get the
problem resolved.
Jerry
--
Jerry Bransford
PP-ASEL KC6TAY
The Zen Hotdog... make me one with everything!
Geezer Jeep: http://www.jjournal.net/jeep/gallery/JBransfordsTJ/
Billy Goten
ASAP and absolutley do not engage 4wd.
"GeoffL" <lawr...@attcanada.net> wrote in
news:038N8.3064$H67....@tor-nn1.netcom.ca:
Billy Goten
to a new tire. Really I cannot believe that people are saying this is
okay. Maybe for a short distance but I wouldn't push it. Most Clubs
require a full size spare for this very reason. Operating your Jeep or any
other 4wd vehicle in this condition is a VERY BAD IDEA.
Jerry Bransford
mismatch in tire size. The problem that rears its ugly head when the
tire sizes are too different from one another is inside the axle with
the differential and there's a locker or LSD inside. A 1" mismatch
won't harm an open differential in the least though. That's why
space-saver spares can be driven as far as they can.
Jerry
--
Billy Goten
I guess I should rephrase my statement to say. I would never operate my
Jeep in this condition, but thats just me. Your advice is as sound as any
but on the side of caution and practical sense I would much rather buy a
new tire than risk any damage to the more expensive innards.
Jerry Bransford <jer...@cox.net> wrote in
news:3D055341...@cox.net:
mad jeep chick
ride with me, since you were so nice as to offer me the same....I sure hope
you like getting really dirty, though. As for that jeep eating tree, well,
that remains to be seen!LOL
Mad Jo
"GeoffL" <lawr...@attcanada.net> wrote in message
news:038N8.3064$H67....@tor-nn1.netcom.ca...
Mike Romain
I gotta check that next time I have my wheels off. I am going to chalk
mark my tires and put my 31" spare on with an aired down to the same
physical height 33".
I think the circumference that the diff gears see does change when a
tire is lowered... I could easily be wrong, but...
I am going to be needing new rear brakes soon and I will test that out.
Hey, Mad Jo in TO is coming over in the next couple days and we have to
pull one of her tires and have her old 215's sitting here. She has
235's on now...
Maybe she will go for being a tire size tester?
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:
Easter/02 http://www.imagestation.com/album/?id=4291929351
Jan/02 http://www.imagestation.com/album/?id=4292141347
Aug/01 http://www.imagestation.com/album/?id=4292076845
Day Trip Misc. http://www.imagestation.com/album/?id=4291902217
Thomas Waldron
pavement to the center of the axle. Now, as the tire rotates, that will
balloon up in the center somewhat at speed, but it still won't be as
tall as when it is filled to proper inflation. It would be a pretty
poor way to match up tire sizes though, but in an emergency, it might
save the differential.
Nonetheless, it's still not a good idea to drive on pavement with a
seriously underinflated tire.
tw
99TJ
01XJ
http://www.jeepn.com/members/html/twaldron.html
Mike Romain wrote:
--
PLEASE REMOVE THE "OBVIOUS" TO REPLY.
Don
> Sure it changes, somewhat. The only measurement that matters is the
> pavement to the center of the axle. Now, as the tire rotates, that will
> balloon up in the center somewhat at speed, but it still won't be as
> tall as when it is filled to proper inflation. It would be a pretty
> poor way to match up tire sizes though, but in an emergency, it might
> save the differential.
>
> Nonetheless, it's still not a good idea to drive on pavement with a
> seriously underinflated tire.
>
Yeah - just ask Ricky Rudd about driving on underinflated tires
Don
Roy Jenson
the axle to the ground. Not that I would reccomend running a tire
at low pressure just to take the load off the differential. Maybe
on a locker for short distances but no where else.
Roy Jenson
that when you make a turn, the rear wheels take a shorter path
than the front wheels and cause all sorts of nasty binding up in
the transfer case and U-Joints. Running one significantly smaller
tire has exactly the smae effect. One driveshaft wants to turn
faster than the other. Most of the time,even 4 tires the same
size will be slightly different due to wear or different
pressures.
L.W.(Bill) Hughes III
It does give a stronger leverage to put to the ground like the
track on a Caterpillar, but, the circumference remains the same. So,
GeoffL's 32" tire would still rotates 630 times in a mile, and the 31"
tire would rotate 650 times, cooking the limited slip.
Mike Romain
flexing out when the air gets lowered and the longer 'footprint'
effectively changes the circumference the axle sees.
I will do an experiment with chalk and mis matched tires soon to see.
Curiosity on this is bugging me.
Mike
Clap Trap
*perimeter*. Circumference is a property of a circle. A loaded tire is not
circular therefore its *circumference* is only an *effective* circumference
defined by its rolling radius.
Lowering the pressure will indeed alter the linear distance traveled for a
360 degree rotation. If you don't believe me, get a set of tinker toys and
put a large wheel on one end of a stick and a smaller wheel on the other.
If you then try to roll that tinker toy axle, it will turn toward the
smaller wheel. If you put a joint between them such that you have two
rotationaly decoupled axle halves, you can then push the axle in a straight
line because the two different size wheels will be able to rotate at
different speeds.
Bottom line, all that matters is that the rolling radius of the two tires
has to be the same in order to prevent a rotational differential between
them. And even then, it only really matters if the axle is locked -
although I would not drive on a significantly different sized spare any
longer than I had too because it also effects braking and steering and can
be disastrous if you're not careful.
"Jerry Bransford" <jer...@cox.net> wrote in message
news:3D05487C...@cox.net...
Clap Trap
you want to see why, do this..... But, if you try this, do it at low speed,
in a wide open parking lot when no one is around.
Put a small diameter tire on one side of the front. Travel in a straight
line. Hit the brakes and see what happens. Again, if you try this - don't
go fast and dont get near anything.
If the mismatch is bad enough, the wheel will jerk to the side of the
smaller tire.
Same thing will happen if you have the same size tires, but with
significantly different backspacing.
Bottom line, if you're worried about blowing a differential, you're worrying
over nothing as long as the rolling radii of the tires are the same. But if
you're running a club and you're worried about liability, or if you're a
manufacturer offering a LSD, require that the spare be the same size so you
don't have some bonehead loose control in a hard stop situation.
"Billy Goten" <asm...@yahoo.com> wrote in message
news:Xns9229DA94B4BBAas...@216.168.3.40...
JustRichie
distance a tire travels.... If you buy into the fact that a tire does not
become physically larger or smaller based on inflation, a tire of a given size
should always travel the same distance in a revolution. The Tinker Toy analogy
compares two objects with different circumference. A more accurate analogy
would be to take a toilet paper roll and roll it one revolution and measure the
distance traveled. Then squish the roll and roll it one revolution. It should
still go the same distance in one revolution. Like a tank tread...the shape is
always changing, but the length is constant.
Is there a flaw in my logic?
Rich
1997 TJ with Sprinkles
http://members.aol.com/justrichie/jeep/index.htm <--Updated 12/20/01
I'm an Environmentalist.
People against off road vehicles are Anti-Recreationalists.
David C. Moller
news:20020611195615...@mb-fd.aol.com...
Nope... that's exactly what I was thinking, but just knew I wouldn't be able
to type it out so good. :)
--
Dave
http://www.msnusers.com/MyJeepWrangler
Gumby
rotation. Yes it rolls completely around the tread with each rotation but
that roll is not round. Clearly an over inflated tire wears out the center
because it is "bigger" than the edge (and each roll covers more ground too).
This must be why we jack up a vehicle to change the flat tire. Happy
Jeeping, I'm glad the fresh air keeps us thinking!
"Clap Trap" <An...@the.net> wrote in message
news:ugd2epk...@corp.supernews.com...
Clap Trap
circumference and then screw up by not properly defining what I meant by
linear distance. For something so simple, this can be quite confusing.
I'll have to come up with a better example before I spout off again. ;)
Nevertheless, the end result is the same - rolling radius is all that
matters. It's left as an exercise for the student because it is intuitively
obvious and the solution is trivial. :-)
"Clap Trap" <An...@the.net> wrote in message
news:ugd1ut4...@corp.supernews.com...
L.W.(Bill) Hughes III
warrantee.
Mike Romain
Tires have sidewalls that drop radically as the pressure lowers. Also
the 'flat' on the bottom will be more like ~ so the 'effective' radius
the axle sees is smaller.
I am going to test this soon. I have a 31" spare with 33" tires and
will be needing brakes soon and need a rotation so when I have the
wheels off I am going to set them up the same height and chalk mark the
tires to see.
First I will run them aired up and see the difference.
I have a feeling that it isn't 'one way or the other' but a middle road
compromise.
Could be wrong, but don't 'think' so.
Mike
Paul Keating
You're right Mike....in the case of a rolling tire, the rolling
circumference is C = 2*Pi*R, so as you decrease R by lowering tire
pressure, you decrease C.
I thought long and hard about this one for a long time and eventually
tried it....the longer center of the tread will scuf badly so it would
not be wise to do outside of an emergency, but the tire will run on
the circumference based on the now shorter sidewall.
Tractech actually specifies this as an acceptable means of using a
mismatched spare with a Detroit locker.
Cheers,
Paul
On Tue, 11 Jun 2002 14:10:00 -0400, Mike Romain <rom...@sympatico.ca>
wrote:
Clap Trap
"L.W.(Bill) Hughes III" <billh...@cox.net> wrote in message
news:3D06A9BF...@cox.net...
EZTarget
Goodyear and a "beat-up but still holds air" factory wheel to use as a spare
for next to nothing. I found a place that only dealt in used tires, they
even bought my factory skinnys and donut.
There has to be an odd used 31" out there somewhere.
--
EZTarget
98 TJ 4cyl, 31"BFG's/AR 767's
"Work in progress" No Chrome, No Stainless......
92 Acura Integra GSR, JDSM B16 conv, 17's
Thomas Waldron
What I said, but you said it FAR better, Paul!
Let's see what Mike comes up with....
tw
99TJ
01XJ
http://www.jeepn.com/members/html/twaldron.html
--
Jerry Bransford
circumference.
Jerry
--
Jerry Bransford
remains the same.
Jerry
--
johnEGp
this theory, and somehow it did, in effect, lower the ratio, but not
enough to actually mean anything.
John in Vegas
Clap Trap
Here's another question for ya......
Assume that your Jeep's odometer has been calibrated such that, at normal
pressure and normal tire size you use, one mile on the odo is exactly one
mile on the ground. Now, go the the start point of your measured mile and
let out all the air in your tires (This is a thought experiment, don't
actually do this). Now drive until your odo reads one mile. Where are you?
If you guys are right and the rolling radius is meaningless, you'll be one
mile down the road, otherwise, you'll come up short.
"Jerry Bransford" <jer...@cox.net> wrote in message
news:3D06CFF1...@cox.net...
L.W.(Bill) Hughes III
resistance destroying your gas mileage along with the tire. The
revolutions of a particular sized tire makes per mile is simple math,
and governed by length of the circumference into that mile.
Thomas Waldron
> Stevie, the rolling radius is meaningless, other than it crates a
> resistance destroying your gas mileage along with the tire. The
> revolutions of a particular sized tire makes per mile is simple math,
> and governed by length of the circumference into that mile.
> God Bless America, Bill O|||||||O
> mailto:LWHug...@aol.com http://www.billhughes.com/
>
I've been having fun with this, but I think it's time to put it to rest.
I admit I've been a party to egging it on, am I a troll now?
This issue is whether or not you get extra tire rotation with a deflated
tire as opposed to a fully inflated tire. Let me propose a simple,
definitive test. It is so simple anyone here can do it.
Make a chalk mark on your driveway or a suitable non-traffic surface,
carry that chalk mark onto a fully inflated tire as if to make one,
straight line at the centerpoint of where the tire rests on the
pavement. Drive one tire revolution and mark the concrete again where
the tire's mark meets the pavement (one revolution).
Since the orig. argument was to use mismatched tires to create an EVEN
situation, to determine if there is a difference in revolution, you must
have BOTH tires on that axle at the same PSI, so deflate BOTH tires on
the same axle a considerable amount, to say to 6psi (don't gouge your
wheels here). Drive BACKWARDS one full revolution, again. Your marks
will line up with the driveway mark, exactly.
Anybody care to confirm this? I'm lazy, but it will put this dead dog
to rest.
Clap Trap
detect low tire pressure.
It is not simple math. The simple math you want to apply to this question
relates to circles, not the deformed shape of a loaded, low pressure tire.
Are you a member of the Flat Earth Society by any chance?
"L.W.(Bill) Hughes III" <billh...@cox.net> wrote in message
news:3D07F52A...@cox.net...
Clap Trap
just let the air out of one. Then drive straight forward until one of them
makes a full revolution. If you guys are right, the marks on both tires
will still be lined up.
"Thomas Waldron" <twaldro...@starband.net> wrote in message
news:3D0804F7...@starband.net...
Clap Trap
www.geocities.com/kpf8655.
Along with this test report, I hereby submit my application for admission
into the Flat Earth Society with heavy sigh and apology for the error of my
previous thoughts.
Mike Romain
I was ready to do the same test and thought correctly that the radius is
the determining factor for the 'effective' distance traveled by a tire.
As someone else pointed out, the makers of one of the lockers say that
lowering the pressure in the larger tire will allow a smaller spare to
be used without blowing up the locker. Same thing for the ABS systems
that can detect a low tire.
Nice research Clap Trap! Thanks.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos:
Easter/02 http://www.imagestation.com/album/?id=4291929351
Jan/02 http://www.imagestation.com/album/?id=4292141347
Aug/01 http://www.imagestation.com/album/?id=4292076845
Day Trip Misc. http://www.imagestation.com/album/?id=4291902217
Clap Trap
opposite, course I could be confused still. One rotation of the tire was
the same forward distance regardless of pressure - recall I had 31x10.50s in
both places, not a large one and a small one. This means 'rolling radius'
did not alter the rotational speed that the axle saw. This means lowering
the pressure on a larger tire would do nothing to help a locker. This
result was a surprise to me precisely because of what the locker company
said, the way the ABS on the Olds Alero is supposed to work, and because
rotational velocity, omega, is equal to the tangential velocity, V, divided
by the radius, r. It is natural to think that the r should be the 'rolling
radius', but this test indicates it is not.
I also repeated the test with a tape mark on the passenger side rear tire.
If the "rolling radius" meant anything, then after one rotation of the
flattened tire, its tape mark would be vertical, but the mark on the full
passenger tire would not. Both marks were vertical.
However, I should also point out that it is obvious as I roll the Jeep that
the flattened tire is trying to slip. It makes squishing noises as it rolls
across the floor where the full tires do not.
But, regardless of the test, if I were on the trail with 33s and needed a
spare and all I had was a friend's 31, I'd still put it on and not worry
about the locker. I just wouldn't run at high speed down the highway with
it.
"Mike Romain" <rom...@sympatico.ca> wrote in message
news:3D092A04...@sympatico.ca...
Mike Romain
Did the tape or chalk marks line up exactly the same after one
revolution?
I thought by the photos that they didn't.
Mike
Thomas Waldron
Nice job, Clappie. The radius changes, but the circumference does not.
You can't change the distance of revolution without changing the
circumference. Unless you deflate the tire enough to create folds that
shorten the circumference, don't risk your axle.
This was fun!
tw
99TJ
01XJ
http://www.jeepn.com/members/html/twaldron.html
--
Clap Trap
a tape measure. However, when rolling back, they were not exact. On a
couple of successive runs, the mismatch continued to get a bit worse.
I think the flattened tire is actually slipping a bit on the floor so that
throws a kink into the question.
I agree, the write up could be better. I've added to it, but it could still
be better.
It's been an interesting topic at the office too - a roomful of engineers
and none of us agree what the answer is. Maybe tomorrow after they see the
results of the test, we can come to a better conclusion.
"Mike Romain" <rom...@sympatico.ca> wrote in message
news:3D094738...@sympatico.ca...
GW De Lacey
>On the initial run, they lined up as close as could be determined with just
>a tape measure. However, when rolling back, they were not exact. On a
>couple of successive runs, the mismatch continued to get a bit worse.
>
>I think the flattened tire is actually slipping a bit on the floor so that
>throws a kink into the question.
>
>I agree, the write up could be better. I've added to it, but it could still
>be better.
>
>It's been an interesting topic at the office too - a roomful of engineers
>and none of us agree what the answer is. Maybe tomorrow after they see the
>results of the test, we can come to a better conclusion.
>
If I might throw a coupla cents worth in here.
The rolling radius is the effective radius, that is the distance
measured from the centre of the wheel to the ground, and this varies
with the amount of pressure in the tyre. That is obvious, and I don't
believe anyone will argue.
This radius behaves no differently to any other radius when the wheel
is rotated, regardless of what's going on around it. Squirming and
scrubbing rubber (when the tyre is deflated) has no effect on the
rolling radius.
The theoretical distance travelled during one revolution of a deflated
tyre is PI times twice the rolling radius. That is, exactly the same
distance as a fully inflated tyre of exactly the same radius
However, the squirming and scrubbing of the deflated tyre has an
unpredictable effect on the actual distance travelled during one
revolution.
Imagine a wheel that has a tyre that's allowed to slip on the rim. In
that case, one revolution could result in zero forward movement (if
trying to go up-hill) or a big uncontrollable amount of forward
movement if trying to go downhill.
In reality, the effect is similar to a tyre that is allowed to slip
for part of the revolution only. If the other part of the revolution
is down hill, the tyre will 'slip' in a way that increases the
distance travelled. The reverse will apply if it's uphill. All sorts
of other effects come into play, and as I said the result is
unpredictable.
The analogy to a caterpillar track is not valid. Because the track is
driven positively by a toothed wheel, the vehicle will move
predictably. The distance travelled per revolution of the driving
wheel is precisely PI times twice the effective radius of the driving
wheel.
Clear as mud?
:))
--
GW DE Lacey
Dead Meat
>Mike, I think you should read it again. I thought I demonstrated just the
>opposite, course I could be confused still. One rotation of the tire was
>the same forward distance regardless of pressure - recall I had 31x10.50s in
>both places, not a large one and a small one. This means 'rolling radius'
>did not alter the rotational speed that the axle saw. This means lowering
Probably because no matter how much pressure is in the tire, there are still "x" inches of rubber
around the circumference of a given tire. A smaller spare tire will turn less than a larger tire
because it has a smaller circumference. It *might* not hurt to travel on a smaller spare, but which
is less expensive, a spare tire (of the right size) or an axle?
...
[snip]
Mike Romain
figured. I took honors physics in university way back when and this one
is bugging me, has been for a while.
I think the radius will affect the 'actual' turns and I also think that
the 'real' circumference will come into play so the 'real' answer should
be somewhere between the pure mathmatics and the pure physical movement
of a tire.
You know, like when you run a tire low on air on pavement it skuffs and
gets hot. Off road the low air is no problem because the speed is low
and the dirt is 'slippery'.
The fact that yours got more and more out every time you rolled it one
rev, implies that something is going on.
And your photos showed the tape vertical, then the tape no longer
vertical.
I think I will have to do a rolling test myself, no offence intended.
We have a RAMJ+W newsgroup run happening this coming Sunday and folks
will be there with air pumps so I will propose a test and we will run a
half dozen revolutions just to see what happens on a trail.
I just BCC'ed this to my mailing list.
I have a digital camera, so we will have shots.
Mike
LXIX
> The tire scuffing is actually part of the equation as far as I had
> figured. I took honors physics in university way back when and this one
> is bugging me, has been for a while.
Scuffing is caused by the tread expanding over the concrete and the
sidewall flexing, any low tire will do that.
> I think the radius will affect the 'actual' turns and I also think that
> the 'real' circumference will come into play so the 'real' answer should
> be somewhere between the pure mathmatics and the pure physical movement
> of a tire.
The actual radius will change somewhat with pressure, but not terribly.
Maby 1/8" at most between max and min pressures.
I played with the math, but you can't just take the radius as the distance
from the axle to the flat spot since your not dealing with a circle anymore
your axis of rotation is not in the center. Long story short the tire
circumferance is the key. Of course I didn't consider any effect of squeezing
on the rubber.
--LXIX--
--LXIX--
Mike Romain
I want to see what 'real life' has to say.
Mike
Clap Trap
of the results.
Also, don't be too surprised about the picts appearing a bit off. They were
done hastily and I did not take care to ensure the camera was perpendicular
to the action. Also, when I started, I figured with the huge difference
between the 80 some odd inch 'effective' circumference and the 91 inch real
circumference, I wouldn't have to be too accurate - I can eyeball to within
those limits.
To throw something else in for you to chew on.....
I redid the test today being a bit more careful and using smaller tape
strips. When the flattened tire's tape mark went 180 degrees around to
vertical on the top, the front tire's tape strip had not yet made it to the
top. It was several degrees off.
The reason I redid the test was because after thinking of approaching the
question from the other end, this difference is to be expected. Consider
that V=wr (where V is tangential velocity, w is omega or rotational
velocity, and r is radius). We know beyond all doubt that the axle shaft is
turning at some w. We also know r from the axle center to the ground.
Therefore, we know V at the point on the ground. Well, one would think that
V is constant in the sense that you'd expect V at the top of the tire to
equal V at the bottom. But, r from the center to the top is different than
r from the center to the bottom. Therefore the velocities at the top and
bottom of the tire are different, very counterintuitive. Think about that
for a while and you will see that at any position other than 0 degrees (the
tire/ground center contact point), the tape marks can't line up.
Consider this scenario also. You are sitting in a chair attached to a
continuous metal band. The band is flat on the floor for a couple of feet
to the front and rear of your chair, but then curves up over your head and
back down. If that band starts turning like the flattened tire, what will
be your velocity? It will be zero until the band lifts you off the floor,
carries your around the partial circumference, and then slams you back into
the floor where your velocity goes back to zero.
Carrying this anology over to the tire, it follows that the velocity of the
tire (of any of the tires in fact) at the ground is the forward velocity of
the Jeep while, for the flattened tire, the velocity at any other
circumferential point is higher.
With all that in mind, I make the following suggestion. If you think in
terms of how a differential works, it is commonly stated that a diff is used
to allow different rotational speeds of the two axle halves and this
statement is what sticks in most people's mind. If you stop right there,
you would conclude from all the above discussion that if the rolling radii
of the tires are the same, the axles have the same rotational velocity, w,
and the diff will see nothing. This was my thinking prior to all this
discussion because I went no further in my considerations.
But, if you continue the study, you will also realize that total forward
distance traveled by the Jeep in one tire rotation is equal to the
circumference of the tire which is constant regardless of pressure.
Consequently, if you have a larger tire on one side, that tire must either
cover more ground in one rotation, or it must slip.
So, the conclusion is that rolling radius governs the rotational velocity,
w, of the axle shafts, nothing more. If one shaft is attached to a bigger
tire, it will turn at the same w as a smaller tire, but for one rotation of
the smaller tire, the larger one will not have yet made a full turn and
consequently, the diff will 'wind up' .
Clear as mud now?
PS - Out of 11 participating engineers who were asked if both tape marks on
my tires we be vertical after the flattened tire made one rotation, 6 said
no and only 5 said yes.
"Mike Romain" <rom...@sympatico.ca> wrote in message
news:3D0A6CF7...@sympatico.ca...
mad jeep chick
"Clap Trap" <An...@the.net> wrote in message
news:ugl424g...@corp.supernews.com...
....<snip>
> Consider this scenario also. You are sitting in a chair attached to a
> continuous metal band. The band is flat on the floor for a couple of feet
> to the front and rear of your chair, but then curves up over your head and
> back down. If that band starts turning like the flattened tire, what will
> be your velocity? It will be zero until the band lifts you off the floor,
> carries your around the partial circumference, and then slams you back
into
> the floor where your velocity goes back to zero.
>
Whoa! Remind me never to volunteer for any of your experiments!
Jo in TO
Clap Trap
While you're listening, let's start another thread - is it possible to drill
a square hole? No experiments needed on this one.
"mad jeep chick" <youcan...@you.dumb.bot> wrote in message
news:SGwO8.40319$_h5.2...@news20.bellglobal.com...
aliasme
but ill take the dunce cap on this one, and agree with everyone of you.
whatever
you answer happens to be.
tim
"Clap Trap" <An...@the.net> wrote in message
news:ugl424g...@corp.supernews.com...
raskal
>:)
>While you're listening, let's start another thread - is it possible to drill
>a square hole? No experiments needed on this one.
I can in wood :-)
Thomas Waldron
The five engineers are correct. The experiment I proposed, and you
essentially realized physically, is only an enigma because you are
applying mathematics for perfect circles which only pertain to fully
inflated tires. Once you deflate the tire, you lose the properties of a
perfect circle, and thus the math is false. Velocity is a red herring
and doesn't enter into the equation other than to show a rotation of the
spheres.
In essence, you have one imperfect sphere and one perfect circle, both
with the same circumference. They will both travel the same distance
in a singular rotation.
Mike Romain
Geese I just got off work and now he wants me to think....
Mike
Clap Trap
Paul Keating
you can buy the appropriate drill bit at any good workworking shop.
my grandfather has a few different sizes...you can see it here.
http://www.leevalley.com/wood/page.asp?page=41702&category=1,180,42334&ccurrency=1&SID=
Cheers,
Paul
On Fri, 14 Jun 2002 22:12:32 -0500, "Clap Trap" <An...@the.net> wrote: